1. Field of the Invention
The present invention relates to a high frequency bandpass filter and, more particularly, to a switchable high frequency bandpass filter, in the field of high frequency communication technology, for providing two high frequency signals having different frequencies with different filter transfer functions, respectively.
2. Description of the Related Art
In today's high frequency communication technology, multi-frequency communication electronic products such as dual-frequency or triple-frequency mobile phones have been developed in order to enlarge an available range of frequency for communication. Typically, it is necessary for multi-frequency communication electronic products to design suitable component circuits in accordance with each of the multiple operational frequencies, thereby satisfying specific requirements of individual operational frequency. As a result, the multi-frequency communication electronic products require a large number of component circuits, not only preventing reduction of size but also increasing production cost.
To reduce the size of the multi-frequency communication electronic products, it is intended that the same component circuits can be commonly employed for multiple operational frequencies so as to minimize the number of necessary component circuits. However, each component circuit has its own distinct high frequency characteristic and therefore cannot be applied to multiple operational frequencies. In other words, if multiple signals with different operational frequencies are commonly processed by the same component circuits, some harmful interference problems may result between the operational frequencies.
For example, a high frequency bandpass filter is generally employed in a high frequency communication system to perform a function of frequency selection. In the multi-frequency communication electronic products, in order to provide each of operational frequencies with an optimum function of frequency selection, it is necessary for every operational frequency to design a dedicated high frequency bandpass filter, thereby providing high frequency signals having different frequencies with different filter transfer functions. However, as described above, such a manner does not only prevent the reduction of size of the multi-frequency communication electronic products but also increases the production cost.